The invention relates to a process for preparing regioregular poly-(3-substituted) thiophenes, selenophenes, thiazoles and selenazoles.
The formidable building block for the development of (micro)electronics during the last one-half of the 20th century is the field-effect transistor (FET) based on inorganic electrodes, insulators, and semiconductors. These materials have proven to be reliable, highly efficient, and with performance that increases periodically according to the well-known Moore's law. Rather than competing with conventional silicon technologies, an organic FET (OFET) based on molecular and polymeric materials may find large scale applications in low-performance memory elements as well as integrated optoelectronic devices, such as pixel drive and switching elements in active-matrix organic light-emitting diode displays, RFID tags, smart-ID tags, and sensors.
As a result of the development of several conductive or semiconductive organic polymers, the application of those as active layer, thus the semiconductor, in organic thin-film transistors (OTFTs) has gained increasing attention.
The use of organic semiconductors in OTFTs has some advantages over the inorganic semiconductors used to date. They can be processed in any form, from the fiber to the film, exhibit a high mechanical flexibility, can be produced at low cost and have a low weight. The significant advantage is, however, the possibility of producing the entire semiconductor component by deposition of the layers from solution on a polymer substrate at atmospheric pressure, for example by printing techniques, such that inexpensively producible FETs are obtained.
The performance of the electronic devices depends essentially on the mobility of the charge carriers in the semiconductor material and the ratio between the current in the on-state and the off-state (on/off ratio). An ideal semiconductor therefore has a minimum conductivity in the switched-off state and a maximum charge carrier mobility in the switched-on state (mobility above 10−3 cm2V−1s−1 on/off ratio above 102). In addition, the semiconductor material has to be relatively stable to oxidation, i.e. has to have a sufficiently high ionization potential, since its oxidative degradation reduces the performance of the component.
In the prior art, a regioregular head-to-tail poly(3-alkylthiophene), in particular poly(3-hexylthiophene) (P3HT) has been suggested for use as semiconducting material, as it shows a charge carrier mobility between 1·10−5 and 0.1 cm2V−1s−1. Regioregular poly(3-alkylthiophene) has shown good performance as the active hole transporting layer in field effect transistors and photovoltaic cells. However, the charge carrier mobility, and hence the performance of these applications, have been shown to be strongly dependent on the regioregularity of the alkyl side chains of the polymer backbone. A high regioregularity means a high degree of head-to-tail couplings and a low amount of head-to-head or tail-to-tail couplings. A high regioregularity leads to good packing of these polymers in the solid state and hence a high charger carrier mobility. Typically a regioregularity greater than 90% is necessary for good performance.
Several methods to produce highly regioregular poly(3-alkylthiophene) have been reported, for example in the review of R. D. McCullough, Ad. Mater., 1998, 10(2), 93-116 and the references cited therein. WO 93/15086 discloses the preparation of highly regioregular poly(3-alkylthiophene) starting from 2,5-dibromo-3-alkylthiophene, wherein the educt is added to a solution of highly reactive “Rieke zinc” (Zn*) to form a mixture of the isomers 2-bromo-3-alkyl-5-(bromozinc)thiophene and 2-(bromozinc)-3-alkyl-5-bromothiophene. The addition of Ni(dppe)Cl2 (1,2-bis(diphenylphosphino)ethane-nickel(II)chloride) as nickel cross-coupling catalyst leads to the formation of a regioregular head-to-tail (HT) poly(3-alkylthiophene).

According to EP 1 028 136, 2,5-dibromo-3-alkylthiophene is reacted with methyl magnesium bromide in THF. The resulting organomagnesium intermediate, which is likewise a mixture of the two regioisomers, is then reacted with a nickel(II) catalyst, Ni(dppe)Cl2, to give the regioregular polymer.

It is an object of the present invention to provide an improved process for preparing a regioregular poly(3-substituted thiophene) or poly(3-substituted selenophene) starting from 3-substituted 2,5-dihalothiophene or 2,5-dihaloselenophene, which gives poly(3-substituted thiophene) or poly(3-substituted selenophene) having a higher regioregularity.